It is well known among electrical engineers that energy losses in dielectric resonator systems occur at contact boundaries, such as those between the dielectric and its support or between the dielectric and the cavity boundary. Energy losses both degrade the efficiency of the resonator by subtracting energy from the system and increase its temperature through resistance heating.
Dielectric resonators are used to confine electromagnetic fields mostly within their boundaries. Dielectric resonators are commonly used in electronic communication devices, such as cellular telephone systems. There is an increasing demand for smaller versions of such systems and other electronic devices. Accordingly, there is a need for smaller dielectric resonators that are capable of the same dielectric performance. Dielectric resonators may be miniaturized by using dielectric elements with higher dielectric constants. The trade-off for the decrease in size of the resonator is that the same amount of power is being drawn through a smaller device. Unless there is an increase in the efficiency of heat removal from the resonator, miniaturization results in the same heat being generated in a smaller volume and a corresponding rise in operating temperatures. It is therefore useful to develop devices exhibiting either less power loss, better thermal dissipation capabilities, or both.
As the temperature of a dielectric element increases, its dielectric constant shifts. Large increases in operating temperatures will therefore result in a shift of the resonant frequency of a dielectric resonator. Temperature differentials and thermal cycling can also contribute to mechanical creep, structural instabilities, component misalignment, debonding, and other undesirable changes in the resonator. It is therefore important to minimize excess heat generated in the resonator, efficiently drain the generated waste heat, and choose components with compatible physical characteristics for use with dielectric element.
In prior dielectric resonator systems, the resonating dielectric element has been secured within its resonant cavity by a variety of mounting media. These include a mounting stem formed as part of the resonating body, adhesives to bond the resonator to a ceramic support and the ceramic support to the casing floor, adhesives to bond the dielectric resonator directly to the casing floor, and insulators to sandwich the dielectric resonator securely within the cavity. Mounting media used in the prior art include media formed from dielectrics, quartz, and plastics. Each of these mounting materials has its own inherent disadvantages.
Adhesives introduce extrinsic energy loss into the system and thereby lower the Q-factor of the resonator. Furthermore, adhesives degrade with time, temperature cycling, and thermal and mechanical shock. Moreover, adhesives introduce assembly inefficiencies because they are cumbersome, messy, and difficult to use with reproducible accuracy. Finally, adhesives tend to be poor thermal conductors and hinder the dissipation of heat from the system.
Some dielectric resonator systems have used quartz to support dielectric element within the resonant cavity. Dielectric element is usually attached to the quartz with an adhesive having all of the disadvantages listed above. Moreover, the coefficients of thermal expansion of the dielectric and the quartz are generally substantially disparate, requiring a flexible adhesive bond to prevent delamination of the adhesive or degradation of the bond.
A mounting stem formed as part of the dielectric resonator does not suffer from the above-mentioned problems associated with adhesives, but can instead distort the electromagnetic field within the cavity. Additional energy loss can be introduced as induced current in the casing. Further, many good dielectric resonators tend to be poor thermal conductors, retarding heat dissipation from the system. Finally, the formation of a one-piece resonator with a stem increases the complexity of the manufacturing process.
Plastic support structures are typically not suitable for use in high temperature applications, as plastic tends to lose structural integrity with increasing temperature. Additionally, plastics typically are poor thermal conductors. Moreover, high-temperature plastics are generally lower-Q materials and contribute to frequency drift with temperature. High-Q plastics, such as high-density polyethylene and high-density polystyrene, quickly lose structural integrity above 100.degree. C.
Finally, the use of sandwiching introduces variables such as stacking tolerances and positioning fluctuations within the cavity with respect to dielectric element.
Hence, there is a need for an improved method of securing the dielectric resonator within the resonant cavity. The securing method must be capable of producing a dielectric resonator system with fewer energy losses and better thermal dissipation, and improved mechanical stability at elevated temperatures. A means for satisfying this need has so far eluded those skilled in the art.